This project examines the physiological basis of the various electrodermal indices and attempts to place them in an adaptive behavioral framework. According to the working model, electrodermal activity consists of two independently-controlled components whose activity can serve a defensive function or can facilitate fine manipulative or tactual exploratory behavior. During defensive behavior copious secretion by the sweat gland would serve to protect the skin against abrasion. This activity is associated with increases in skin conductance and in negative skin potential which are slow to recover. During fine manipulation or tactual exploration an epidermal mechanism, associated with the positive skin potential response, comes into play to control hydration at an optimal level in relation to the coefficient of friction of the skin surface or to its characteristics as a tactile mechano-transducer. This control is believed to be mediated by reflex reabsorption of sweat. Reabsorption accelerates recovery of the skin conductance response and the recovery limb time constant has been found to be a remarkably sensitive behavioral indicator, faster recoveries being associated with goal-directed set, higher rates of cognitive performance, fewer errors and greater attention. When retarded recovery occurs in the presence of increased electrodermal activity, it appears to signal an aversive response and inhibition of reabsorption. This project, in addition to examining physiological behavioral relations, attempts to develop methods for quantitative assessment of reabsorption.